One possible way is to make use of the API CyBle_GapcStartDiscovery with the updated scan parameters (referenced by CYBLE_GAPC_DISC_INFO_T* scanInfo). You can update the scanInfo structure with the new parameters. First stop scan, then update the parameters and then call CyBle_GapcStartDiscovery.

CYBLE_EVT_GATTC_DISCOVERY_COMPLETE is generated when the remote device was successfully discovered. Can you check if it enters the even CYBLE_EVT_GATTC_ERROR_RSP?